Feeding device and image forming apparatus

Abstract

A feeding device includes: a sheet material housing configured to allow a plurality of sheet materials to be stacked; an upper surface suction unit that sucks a top sheet material by generating negative pressure at a position facing the upper surface of the top sheet material; a sheet material conveying unit that causes the top sheet material, which is sucked up, to be sucked onto a conveying member and conveys the top sheet material; and a lower suction unit that exerts a suction force downward onto the sheet materials that are positioned near the top sheet material, wherein a suction force exerted on the top sheet material downward by suction of the lower suction unit is smaller than a suction force exerted on the top sheet material upward by suction of the upper surface suction unit and is larger than adhesion between the sheet materials.

What is claimed is: 
     
       1. A feeding device comprising:
 a sheet material housing configured to allow a plurality of sheet materials to be stacked; 
 an upper surface suction unit configured to suck a top sheet material which is positioned at the top of sheet materials stacked in the sheet material housing by generating negative pressure at a position facing an upper surface of the top sheet material; 
 a sheet material conveying unit that causes the top sheet material, which is sucked by the upper surface suction unit, to be sucked onto a conveying member and conveys the top sheet material to a subsequent process; 
 a lower suction unit that exerts a downward suction force on only a central portion of the sheet materials other than the top sheet material that are stacked in the sheet material housing; and 
 at least one air discharge unit configured to cause lateral side portions of the top sheet material and lateral side portions of each of other sheet materials positioned near the top sheet material to be concurrently floated higher than the central portion of the sheet materials other than the top sheet material that are stacked in the sheet material housing by blowing air to each of a plurality of lateral side portions of the sheet materials that are positioned near the top sheet material of the sheet materials stacked in the sheet material housing concurrently, wherein 
 a downward suction force which is exerted on the top sheet material by suction of the lower suction unit is smaller than a suction force which is exerted on the top sheet material by suction of the upper surface suction unit and is larger than an adhesive force between the sheet materials, 
 the lower suction unit is configured to suck a front end portion of a plurality of the sheet materials, which are positioned near the top sheet material, downward concurrently, while the top sheet material being sucked by the upper surface suction unit so as to just start to float upward and while portions lateral to the central portion are being blown upwardly by the at least one air discharge unit, and 
 the lower suction unit is directly connected to a suction nozzle located on a front wall of the sheet material housing facing the front end portion of the sheet materials and between air discharge nozzles located on the front wall and connected to the at least one air discharge unit. 
 
     
     
       2. The feeding device according to  claim 1 , further comprising:
 a sheet material blocking member configured to block a leading edge of the sheet materials other than the top sheet material 
 when the sheet material conveying unit conveys the top sheet material and 
 when the sheet materials start to be conveyed together with the top sheet material. 
 
     
     
       3. The feeding device according to  claim 2 ,
 wherein 
 a suction portion of the lower suction unit is in contact with the sheet material blocking member, and 
 a width of an opening of the suction portion is larger than a width of a portion of the sheet material blocking member that is in contact with the suction portion. 
 
     
     
       4. The feeding device according to  claim 2 ,
 wherein a suction portion of the lower suction unit is formed integrally with the sheet material blocking member. 
 
     
     
       5. The feeding device according to  claim 1 ,
 wherein air, which is sucked in by the lower suction unit, is discharged out from the air discharge unit. 
 
     
     
       6. The feeding device according to  claim 1 , further comprising:
 a sheet upper surface position detecting unit that detects a height of the upper surface of the top sheet material; 
 a bottom plate that supports a lower surface of the sheet materials stacked in the sheet material housing; 
 a lifting unit that lifts the bottom plate up and down in a vertical direction; and 
 a lifting control unit that controls an operation of the lifting unit so that the height of the upper surface of the top sheet material of the sheet materials supported on the bottom plate becomes a predetermined height, based on a detection result from the sheet upper surface position detecting unit. 
 
     
     
       7. An image forming apparatus comprising:
 an image forming section that forms an image on a sheet material that is a recording medium; and 
 a sheet material feeding unit that feeds the sheet material to the image forming section, 
 wherein the feeding device according to  claim 1  is used as the sheet material feeding unit. 
 
     
     
       8. The feeding device according to  claim 3 , wherein the sheet material blocking member covers at least a portion of the opening of the suction portion of the lower suction unit. 
     
     
       9. The feeding device according to  claim 1 , wherein the downward suction force of the lower suction unit is greater than sheet separation force of the at least one discharge unit.